In electronic color imaging, it is desirable to simultaneously capture image data in three color planes, usually red, green and blue. When the three color planes are combined, it is possible to create high-quality color images. Capturing these three sets of image data can be done in a number of ways. In electronic photography, this is sometimes accomplished by using a single two dimensional array of sensors that are covered by a pattern of red, green and blue filters. This type of sensor is known as a color filter array or CFA. Below is shown the red (R), green (G) and blue (B) pixels as are commonly arranged on a CFA sensor.
When a color image is captured using a CFA, it is necessary to interpolate the red, green and blue values so that there is an estimate of all three color values for each sensor location. Once the interpolation is done, each picture element, or pixel, has three color values and can be processed by a variety of known image processing techniques depending on the needs of the system. Some examples of the reasons for processing are to do image sharpening, color correction or half toning.
The diagram below shows how red green and blue pixels can be arranged in a particular color filter array pattern, hereinafter referred to as the Bayer color filter array. For a more detailed description see U.S. Pat. No. 3,971,065 issued Jul. 20, 1976 to Bayer.
______________________________________ G R G R B G B G G R G R B G B G ______________________________________
In commonly assigned U.S. Ser. No. 08/606,112 filed Feb. 23, 1996 entitled "Adaptive Color Plane Interpolation in Single Sensor Color Electronic Camera" to Adams et al and commonly assigned U.S. Ser. No. 08/606,178 filed Feb. 23, 1996 entitled "Averaging Green Values for Green Photosistes in Electronic Cameras" to Hamilton et al adaptive methods of calculating green pixel values at pixels where green is not directly measured is described, the teachings of which are incorporated herein by reference. These methods produce better reconstructions for horizontal and vertical features than they are for diagonal features in the image. This is because there are green pixels in every row and every column of the CFA. However, every other diagonal in the CFA is devoid of green pixels. With this arrangement, the frequency response on diagonals is less than that on horizontal rows and vertical columns. As a consequence, diagonal edges are less sharp than horizontal and vertical edges. Moreover, interpolation of green values in the diagonal direction is not available. It would be desirable to have a CFA pattern in which diagonal interpolation, in addition to horizontal and vertical interpolation, would be available.